The present invention relates to improved articles of footwear particularly socks and inserts.
The problem of wet feet has plagued mankind since the dawn of history. Many attempts have been made to keep feet dry. The problem, however, is not as simple as just keeping the foot away from liquid water. This can be temporarily achieved by a variety of water impervious materials such as rubber boots. These forms of footwear are uncomfortable because, while they keep water from external sources away from the foot, they do not let perspiration escape. The result is that the foot becomes damp from perspiration. There was a need for a material that was both waterproof and breathable. U.S. Pat. No. 3,953,566 discloses a method of making a form of expanded polytetrafluoroethylene (PTFE) that possesses the contradictory properties of being both breathable and waterproof. U.S. Pat. No. 4,194,041 discloses an improvement on the material described in U.S. Pat. No. 3,953,566. The materials of both of these patents have been widely used in waterproof, breathable outdoor wear, including footwear, such as boots and socks.
While these materials were effective for their purpose, they had very little stretchability, generally less than 5%. This caused a problem in that, if the sock was designed to fit snugly when worn, it was very difficult to put on. If the sock was designed to be put on easily, it was too large when placed on the foot. U.S. Pat. No. 4,443,511 discloses a method of making stretchable, elastic, expanded PTFE material, thus providing a material that could be stretched up to 130%. Bunching is not normally a sock problem because a gentle pull smooths the fabric and the elastic recovery redistributes it over the heel and ankle. Conventional socks gradually abraid away, generally at the heel and toe, culminating in catastrophic failure. With the unique materials described in U.S. Pat. No. 4,443,511, the rubbing or buckling and tensioning of the material associated with bunching, typically under great pressure between the back stay, heel counter and topline of the footwear, prematurely induces holes and cracks in the membrane, greatly reducing the value of the product. Special donning and doffing instructions, followed carefully, can prevent this failure. A significant improvement is achieved by "rolling" the sock on. Socks and footwear have been made from this material, but they have proved not to be completely satisfactory because abrasion problems develop in the heel area. Above the heel, leaks can develop when a 100% stretch sock is put on improperly, i.e. stretched too much by not "rolling" the sock on.